1. Field of the Invention
The present invention relates generally to a device and a method, as well as uses thereof, of a Variable Optical Attenuator (VOA), and specially for controlling the intensity of light in an optical fiber by use of a tunable dynamic grating in a optical communication systems.
2. Description of the Related Art
The demand for bandwidth for communication and information exchange has been growing exponentially. The growth has particularly accelerated by the introduction of Wavelength Division Multiplexing (WDM) technology used to multiplex optical signals along the same optical fiber by use of different wavelengths in narrow bands with minimal dissipation. Active components are needed in addition to the passive fibers, in order to generate, amplify, route, and filter signals. This has lead to the development of a wide range of technologies to manipulate light in optical fibers, such optical components includes filters, switches, amplifiers, and attenuators. However, the high cost of components, in particular for the more advanced components including many subparts, are inhibiting the speed of deployment of optical communication systems, and the introduction of all optical networks. Consequently, it is necessary to develop cost effective components that have the necessary specifications, but allow low cost assembly and production method to be used. Optical communication systems are used in telecommunication systems, local area networks, wide area networks, television networks, instrumentation networks, etc. and all other types of communication systems where communicating symbols, messages and signals and its like is best provided for by optical means.
A component of particular demand in fiber optical communication systems is the variable optical attenuator. Attenuators are used as stand-along components for example to compensate for aging effects in other components, and to avoid saturation of detectors. However, for a more dynamic network structures, such as in an all-optical network, the signal strengths in the system from various sources or from various pathways will vary widely, and the need for reconfigurable or dynamic variable optical attenuators arise. Variable optical attenuators are also an important subpart of modules such as equalizers and optical add/drop multiplexers. For such applications, it is particularly the scalability of the technology that will determine the end price of the module.
Several embodiments have been suggested for tunable diffraction gratings with applications to fiber optical components. One of the known methods is diffractive MEMS (D-MEMS). This technology is available from Light Connect and Silicon Light Machines, for example. These devices are based on a moveable diffraction grating consisting of at least two separate pieces. A stationary reflective bottom surface, a moveable set of thin blades, and the grating are made of etched silicon. The blades can be moved up and down by the application of an appropriate electrical field. The result is a diffraction grating, where the effective phase shift of the grating is given by the relative position of the blades and the reflective surface below. This allows the grating to be turned on and off with a response time of only a few milliseconds. However, the voltages required to displace the blades are still high, on the order of tens to hundreds of Volts. This arrangement can be used to make effective variable optical attenuators, but the set of blades must be processed out of silicon. This is an expensive process, and the yield of the process goes dramatically down as the system size is increased. Components made from D-MEMS are hence effective, but expensive.